Human activity task is now shown (after change of user provider?)

I have a quite old process (created in April) which I don't use very often, but recently it stopped showing task created by Human activity. There was no change in this area in the process itself. To be sure, I have debugged and checked that UserId of Human activity = 4 and Session.UserId = 4 when I'm logged in. In service center, it shows that the process is on that task stage and there is no error, which means the task is created. Logging out and back still doesn't show any task. And I have checked in different applications (it used to be shown everywhere).

There was a change some time ago - we changed user provider from the default Users to own own eSpace everywhere. I think this is related to this, at least I can't think out any other reason.